This invention relates to a heat-sensitive transfer material which can give a transfer-recorded image of good printed letter quality even on a recording medium with poor surface smoothness, and to a heat-sensitive transfer recording method using the same.
With rapid progress of information industries in recent years, various information processing systems have been developed, and various recording methods and devices suited for the respective information processing systems have been developed and adopted. As one of such recording methods, the heat-sensitive recording method has recently been widely used because of various advantages such as that the apparatus therefor is light in weight and compact, does not generate noise and also is excellent in operability and maintenance.
However, of the recording papers used for the heat-sensitive recording method, ordinary heat-sensitive recording papers are expensive since they are converted papers containing a color forming agent and a developing agent, and also involve the problems that alteration of the recording is possible, that the recording paper is susceptible to color formation by heat or organic solvents and that the storability of recording is poor, since a recorded image fades within a relatively short time.
As the method which maintains the advantages of the heat-sensitive recording method as described above and also compensates for the disadvantages of using heat-sensitive recording papers, the heat-sensitive transfer recording method is particularly attracting attention in these days.
In the heat-sensitive recording method, a heat-sensitive transfer material is used, which comprises a heat-transferable ink containing a colorant dispersed in a heat-fusible binder coated by melting on a support generally in the form of a sheet and the recording is generally conducted by superposing the heat-sensitive material on a recording medium such as paper so that the heat-transferable ink layer will contact the recording medium, supplying heat from the support side of the heat-sensitive transfer material by means of a thermal head to transfer the molten ink layer to the recording medium, thereby forming a transferred ink image corresponding to the heat supplying pattern on the recording medium. According to this method, the advantages of the heat-sensitive recording method as mentioned above can be maintained, and also the disadvantages with the use of the heat-sensitive recording paper can be eliminated.
However, the heat-sensitive transfer recording method of the prior art is not free from drawbacks. That is, according to the heat-sensitive transfer recording method of the prior art, the transfer recording performance, namely the printed letter quality, is remarkably influenced by the surface smoothness of the recording medium, and therefore while good printing can be effected on a recording medium having high smoothness, the printed letter quality will be markedly lowered in the case of a paper with low smoothness. However, even when paper which is the most typical recording medium may be used, a paper with high smoothness is rather special and ordinary papers have surface unevenness to various extents because they are formed through entanglements of fibers. Accordingly, in the case of a paper with large surface unevenness, the heat-molten ink cannot penetrates into fibers during printing but attaches only on the convexities or in the vicinity thereof on the surface, as a result of which the printed image may not be sharp at the edge portion or a part of the image may be missing, lowering the printed letter quality. Also, for improvement of the printed letter quality, it may be considered to use a heat-fusible binder with a low melting point. In this case, however, the heat transferable ink layer becomes tacky also at a relatively lower temperature, whereby inconveniences such as lowering in storability and staining at the non-printed portion may occur.
For the purpose of removing inconveniences such as defects or imperfections of printed letters without inviting such lowering in storability, the amount of heat supplied may be increased and heating time may be prolonged. Although imperfection of printed letters may be avoided by employment of such measures, lowering in recording sensitivity or in heat transfer speed may be caused, and further the printed letters will contrariwise become too bold, reducing the clearness of the recorded image.